Obstructive sleep apnea (OSA) is a highly prevalent condition in hypertensive patients. The renin-angiotension-aldosterone-system (RAAS) has a central role in blood pressure control. An angiotensin-II-antagonist, Losartan, is an effective antihypertensive drug. However, some patients respond to this drug worse than the others, and it is a clinical praxis to either increase the dosage and/or add another drug. There is limited data regarding the impact of antihypertensive drugs in OSA patients, i.e., whether or not OSA may constitute the subgroup of therapy-resistent hypertensive patients. In the literature, there is no data, either, whether or not CPAP treatment may have an additive blood pressure lowering impact in this certain subgroup.

OSA is a highly prevalent condition in hypertensive patients and the prevalence is even higher in patients with drug-resistant hypertension. The renin-angiotension-aldosterone-system (RAAS) has a central role in blood pressure control. An angiotensin-II-antagonist, Losartan, has an effective antihypertensive drug. However, some patients respond to this drug worse than the others, and it is a clinical praxis to either increase the dosage and/or add another drug. There is limited data regarding the impact of antihypertensive drugs in OSA patients, i.e., whether or not OSA may constitute the subgroup of therapy-resistent hypertensive patients. In the literature, there is no data, either, whether or not CPAP treatment may have an additive blood pressure lowering impact in this certain subgroup. The investigators will include 90 otherwise healthy, untreated hypertensive men and women(age 50-69 yrs, Body-Mass-Index <35 kg/m2; 60 patients with OSA, 30 non-OSA) as described above. Before start of treatment, fasting blood samples will be drawn regarding the neuroendocrine hormones (adrenaline, noradrenaline, plasma renin activity, angiotensin II,aldosterone, pro-BNP) and cardiovascular biomarkers (CRP,interleukines, cytokines). All subjects will start with Losartan 50 mg and 24 h- blood-pressure response and blood sample analysis will be compared between OSA and non-OSA subjects after 6 weeks of treatment. In the second 6-week period, all subjects will continue with Losartan while the half of the OSA group (n=30) will be randomized to CPAP and the other 30 patients will continue with Losartan only.

Inclusion Criteria:

• Body Mass Index <35 kg/m2
• Systolic Blood Pressure >=140 mmHg and/or Diastolic Blood Pressure >=95 mmHg
• No known clinical disease except hypertension
• No cardiovascular medication
• Apnea-Hypopnea Index < 5/h (no OSA), or Apnea Hypopnea Index >=15/h (OSA)

Exclusion Criteria:

• Manifest diabetes, liver- or kidney disease Signs of atrial fibrillation or former myocardial infarction at electrocardiogram